Transformer circuits



April 21, 1925.

1,534,086 E. o. SCRIVEN TRANSFORMER CIRCUITS Filed Aug. 8, 1922frequency I 40aa- 20aa- I 6000- l Patented Apr. 21, 1925.,

UNITED STATES PATENT OFFICE.

EDWARD O. SCRIVEN, OF NEW YORK, N. Y., ASSIGNOR 'IO WESTERN ELECTRICCOM- PANY, INCORPORATED, OF NEW" YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSFORMER CIRCUITS.

Application filed August 8, 1922. Serial No. 580,532.

" transformer circuits and particularly to transformers employed toinductively couple a vacuum tube repeater to a source of 1mvpulses to berepeated.

In certain amplifier circuits an input transformer has heretofore beenemployed with which has been associated either an actual inductance orleakage inductance of a value to resonate with the vacuum tube electrodecapacities and the capacities between the turns of the secondary Windingat a frequency near or above the upper limit of the essential speechrange. The effect of this arrangement is to increase the transmissionthrough the amplifier at the higher frequencies, which would otherwisebe attenuated by the shunt capacities referred to.

It has sometimes been found in cases where filters are not employed thatsufficient energy is transmitted at or near the resonant frequency tocause singing of the amplifier.

An object of this invention is to reduce the transmission at the higherfrequencies in transformer circuits of the above type and therebyprevent singing.

Another object is to obtain an effective balance of capacities in atransformer in which one winding is superimposed on another.

In the embodiment of the invention shown herein, a two-stage amplifiercomprises one vacuum tube inthe first stage and two oppositely connectedtubes in the second stage. A transformer, which is employed to connectthe two stages, comprises a single primary winding and two secondarywindings superimposed thereon. The outer terminal of the primary and thejunction of the secondaries are connected to ground.

The inner layer of the innermost secondary has a capacity to the primaryand therefore to ground. This capacity is thus effectively in shunt tothe innermost secondary and is added to the shunt capacity of the tubeconnected across that winding. In accordance with this invention a smallcondenser is connected between ground and the outer layer or .ungroundedterminal of the outermost secondary. This condenser serves to balancethe natural capacity of the innermost secondary and serves also toincrease the shunt capacity and thereby reduce the gain and the dangerof singing at the upper audible frequencies.

Fig. 1 represents diagrammatically an amplifier circuit embodying theinvention.

Fig. 2 represents diagrammatically the arrangement of windings of theinterstage transformer.

Fig. 3 represents graphically the efl'cct 'of using the invention.

An input transformer is adjustably connected by switch 12 to a Vacuumtube amplifier 14. Interstage transformer 16 connects tube 14 toamplifier tubes 18 and 20 of the second stage, the latter beingconnected oppositely, or in push-pull relation. Output transformer 22serves to impress the amplified energy upon any desired work circuit.The grids of the tubes are rendered negative by battery 24. Thefilaments are heated by batteries 25 and 26 in series. Space current issupplied by battery 27. The circuit is grounded at 28.

Transformer 16 comprises a primary winding 29 and secondary windings 30and 31. The junction of windings 30 and 31 is connected to groundthrough battery Transformer 16 is designed to-have leakage inductancerepresented {in the drawing as series inductances 33. Actual inductancemay, of course, be employed if desired. This effective series inductanceforms a resonant circuit with the capacities of the tubes in the secondstage and with the capacities between the turns of a secondary windingat a frequency in the upper part of the voice range and increases thetransmission at the higher frequencies Where it would otherwise fall offdue to the shunt capacities. 1

It has been found, vas above stated, that the transmission issometimes'great enough to produce singing-at the vresonant frequency. thas further been found that by increasing the shunt capacity an effectis obtained which appears to correspond to'reducing the cut-offfrequency ofa filter.

In Fig. 3, curve A represents the transmission' of the circuit with onlynatural capacities present; curve B represents the ondary winding 31 toground, while curve C represents the transmission using a slightlylarger value of condenser 32. It'

will be noted that in curves B and C the maximum amplification is muchless than in curve A for the high unessential frequencies, while thereis no substantial reduction for the essential frequencies of speech andmusic.

Referring to Fig. 2, the manner in which the increase in shuntcapacityis obtained will be understood. It is seen that the natural capacity36'is efi'ectively connected through ground across secondary winding 30.Condenser 32 is in substantially the same relation to winding 31. Asymmetrical arrangement thus is obtained in which the capacities 32 and36 cooperate to elinnnate danger of sin ing.

The invention c aimed is;

1. A transformer comprising a winding having its outer layer connectedto ground, a second winding superimposed on said first winding andhaving its outer layer connected to ground, a third winding superimposedon said second winding and having its inner layer connected to ground,and a condenser connected between ground and the outer layer of saidthird winding.

2. In an electric circuit, a line, a transformer comprising a primaryand two secondary windings, sai secondary windings being connectedsymmetrically as to the two sides of said line, the physical arrangementof said secondary windings being unsymmetrical whereby one of saidsecondary windings has a greater capacity to said primary winding thanthe other, and a capacity between said other secondary winding and saidprimary winding.

3. A transformer com rising several windings-two of said win ings beingserially connected, one of said two windings having greater capacitythan the other to a third of said windings, and a path comprising acondenser connecting said other winding to saidthird winding.

4:- In combination, a transformer having two secondary windings, twovacuum tubes having cathodes connected together and to the adjacentterminals of said windings,

and having control electrodes connected to the non-adjacent terminals ofsaid windings, one of said control electrodes bein connected to saidcathodes through a pat 1 comprising a natural capacity in saidtransformer, and a path comprising a condenser connecting the other ofsaid control electrodes to said cathodes.

5. A transformer comprising a multilayer primary and two multi-layersecondary windings, the layer of said primary winding adjacent to one ofsaid secondary windings, and the junction of said secondary windingsbeing connected to ground through paths of low impedance whereby thenatural capacity between the adjacent layer of said primary winding andone of said secondary windings is effectively connectedin shunt tosaidsecondary winding, and a-capacityconnected between the terminalofthe non-adjacent layer of the other "of said secondary windings andground for efiectively balancing said natural capacity.

6. In combination, a vacuum tube ampli-- fier having input electrodes,an input transformer therefor, said transformer having a primary windingand a secondary winding superimposed thereon, and means for connectingthe natural capacity between said windings effectively in shunt to saidsecondary winding and to said input electrodes. v I I 7 In combination,a multi-stage amplifier comprising a vacuum tube, a transformer havingits primary winding-in the output circuit of said vacuum tube, the outerterminal of said winding being connected to ground through a path of lowimpedance, the secondary of said transformer comprising two windingssuperimposed in order on said primary winding, two vacuum tubes havingtheir cathodes connected to ground and to the adjacent terminals of saidsecondary windings, and having their control electrodes connected to thenon-adjacent terminals thereof, and a condenserin a path in shunt to theouter of said windings.

In witness whereof, I hereunto subscribe my name this 2nd day of AugustA. 1).,

EDWARD O. SCRIVEN.

